The present invention relates generally to semiconductor package technology, and more particularly to a unique manufacturing methodology for a semiconductor package wherein singulation is accomplished by etching as opposed to mechanical cutting (e.g, sawing or punching).
Integrated circuit dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and an underlying substrate such as printed circuit board (PCB). The elements of such a package include a metal leadframe, an integrated circuit die, bonding material to attach the integrated circuit die to the leadframe, bond wires which electrically connect pads on the integrated circuit die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior of the package often referred to as the package body. In a cavity type semiconductor package, the package body is substituted with a prefabricated cavity which is formed on the leadframe, the die being positioned within the cavity and sealed therein by a lid or similar structure which is attached to the cavity.
The leadframe is typically the central supporting structure of a semiconductor package. A portion of the leadframe is internal to the package, i.e., completely surrounded by the plastic encapsulant package body or the prefabricated cavity. Portions of the leads of the leadframe extend externally from the package or are partially exposed within the package body or cavity for use in electrically connecting the package to another component. In certain semiconductor packages, a portion of the die pad of the leadframe also remains exposed within the package body for use as a heat sink.
For purposes of high volume, low cost production of semiconductor packages, a current industry practice is to etch or stamp a thin sheet of metal material to form a panel or strip which defines multiple leadframes. A single strip may be formed to include multiple arrays, with each such array including a multiplicity of leadframes in a particular pattern. In a typical semiconductor package manufacturing process, integrated circuit dies are mounted and wire bonded to respective ones of the leadframes, with the encapsulant material then being applied to the strip so as to encapsulate the integrated circuit dies, bond wires, and portions of each of the leadframes in the above-described manner. The hardening of the encapsulant material facilitates the formation of a mold cap upon the leadframes.
Upon the hardening of the encapsulant material, the leadframes within the strip are cut apart or singulated for purposes of producing the individual semiconductor packages. Such singulation is typically accomplished via a saw singulation process or a mechanical punching operation. In the saw singulation process, a saw blade is advanced along “saw streets” which extend in prescribed patterns between the leadframes as required to facilitate the separation of the leadframes from each other in the required manner. The advancement of the saw blade along the saw streets currently cuts the molded plastic mold cap, thus facilitating the formation of the above-described molded plastic package body upon each of the separated leadframes. With particular regard to cavity type semiconductor packages, the saw blade is advanced along the saw streets which typically extend between the various cavities formed on the strip.
One of the drawbacks associated with the saw singulation process used in relation to the manufacture of semiconductor packages is that the saw blade used in the saw singulation process cuts through copper (i.e., the metal material typically used to fabricate the strip) usually most of the time. As will be recognized, this level of sawing through copper as occurs as a result of the configuration of the strip often results in the premature wear of the costly saw singulation blades. Another drawback of the saw singulation process is that the same also typically results in the burring of the leads of the separated leadframes. Saw generated burrs at the leads often adversely affect solder mounting and joint reliability. In current semiconductor package fabrication methodologies, lead burrs are often controlled by limiting the feed rate of the saw blade along the saw streets and by using specifically developed, high cost saw blades. However, as will be recognized, the use of the high cost saw blades is undesirable due to the resultant increase in production cost, with the reduced feed rates needed to control burring also adversely affecting production speed, and thus efficiency. With particular regard to the punch singulation process, one of the drawbacks associated with the use of such process is the tendency for the hardened encapsulant material or package body of the semiconductor package to chip or crack as a result of the punching operation. As will be recognized, such chipping or cracking of the package body can result in the accelerated failure thereof as a result of, among other things, moisture permeation to the embedded integrated circuit die. Further, punch singulation is typically not preferred for applications using mechanically sensitive die due to the perceived risk associated with impact vibration (e.g., MEMS).
The present invention addresses the above-described drawbacks by providing a semiconductor package having structural attributes which are uniquely tailored such that the singulation process is achieved using etching techniques. Advantageously, etching techniques are inherently lower in cost and free from many of the defects induced by other cutting techniques (e.g., sawing, punching) as highlighted above. These, and other advantages of the present invention, will be discussed in more detail below.